Loans and Allowance for Credit Losses - Schedule of Recorded Investment in Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment	$ 9,017	$ 8,346
Allowance for loan losses, Ending balance: collectively evaluated for impairment	33,889	32,378
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	1,762	2,569
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	1,484	3,852
Total allowance for credit losses	46,152	47,145
Loans and leases outstanding, Ending balance: individually evaluated for impairment	78,468	69,210
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	5,324,426	4,841,719
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	39,825	37,145
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	96,149	134,890
Total loans	5,538,868	5,082,964	5,176,222
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment	6,320	6,156
Allowance for loan losses, Ending balance: collectively evaluated for impairment	11,555	9,980
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	252	429
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	699
Total allowance for credit losses	18,826	16,565
Loans and leases outstanding, Ending balance: individually evaluated for impairment	37,657	34,213
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	1,471,425	1,355,608
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	2,506	648
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	8,889	12,281
Total loans	1,520,477	1,402,750
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment	2,697	2,190
Allowance for loan losses, Ending balance: collectively evaluated for impairment	13,292	14,816
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	1,255	2,025
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	520	3,370
Total allowance for credit losses	17,764	22,401
Loans and leases outstanding, Ending balance: individually evaluated for impairment	40,811	34,997
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	1,289,817	1,106,971
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	27,654	23,618
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	47,432	77,232
Total loans	1,405,714	1,242,818
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: collectively evaluated for impairment	5,509	4,494
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	215	80
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	265	366
Total allowance for credit losses	5,989	4,940
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	1,138,009	1,019,576
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	9,509	12,725
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	14,988	17,673
Total loans	1,162,506	1,049,974
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: collectively evaluated for impairment	3,533	3,088
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	40	35
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality		116
Total allowance for credit losses	3,573	3,239
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	1,425,175	1,359,564
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	156	154
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	24,840	27,704
Total loans	1,450,171	1,387,422
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment
Allowance for loan losses, Ending balance: collectively evaluated for impairment
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality
Total allowance for credit losses
Loans and leases outstanding, Ending balance: individually evaluated for impairment
Loans and leases outstanding, Ending balance: collectively evaluated for impairment
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality
Total loans